Researchers in Tasmania say they have found evidence of a biological link between diet and depression, via a study that analysed associations between diet, BMI, inflammatory markers, and mental health in adolescents.

The association between depression and being overweight / obese is known, but this new research, led by Professor Wendy Oddy from the Menzies Institute for Medical Research at the University of Tasmania and involving participants from the Western Australian Pregnancy Cohort (Raine) Study, focused on a possible biological pathway.

The study found that diet and obesity werelinked to inflammation and mental health problems in adolescents, while a 'healthy' dietary pattern (high intake of fruit, vegetables, fish and whole grains) protected against depression in adolescents through reduced BMI and associated inflammation.

The researchers also discovered that a Western dietary pattern (high intake of red meat, refined and takeaway foods, confectionery) was associated with increased depression risk in adolescents, most likely through increased BMI and underlying inflammation.

Approximately 1,600 Raine Study participants were surveyed at the age of 14 years, and more than 1,000 at 17 years, for the study.

Questionnaire answers on food and nutrient intake at 14 years were cross-referenced with a mental health questionnaire and clinical data on BMI and inflammation three years later.

Biological mechanism

People in the study were asked about their usual dietary intake in the past year, and their diet was classified as either mainly 'healthy' or 'Western'.

Withdrawal, social problems, anxiety, depression and physical symptoms were assessed by a mental health questionnaire.

Professor Oddy said the research indicated a complex association between dietary patterns, being overweight / obese, inflammation, and mental health problems, including depressive symptoms.

"Scientific work on the relationship between mental health problems and inflammation is still in its infancy, but this study makes an important contribution to mapping out how what you eat impacts on these relationships,"​ she said.

Professor Oddy said her team of researchers is now studying specific food components and nutrients to try to understand more about the biological mechanisms leading to mental health problems and depression in adolescents and young adults.

The paper concluded: "A 'Western' dietary pattern associates with an increased risk of mental health problems, including depressive symptoms in adolescents, through biologically plausible pathways of adiposity and inflammation, whereas a 'healthy' dietary pattern appears protective in these pathways.​

"Longitudinal modelling into adulthood is indicated to confirm the complex associations of dietary patterns, adiposity, inflammation, and mental health problems, including depressive symptoms."​